This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This is a multiphase, multicenter, trial that will comprehensively examine lithium in the treatment of pediatric patients with bipolar I disorder. This study includes four treatment phases, including a pharmacokinetic phase, a long-term effectiveness phase, a discontinuation phase and a restabilization phase.